JPH05-005658U published by the Japan Patent Office in 1993 discloses a hydraulic pressure supply device which supplies pressurized working oil to a power steering device and a cargo handling device of an industrial vehicle such as a fork-lift truck, from a single hydraulic pump via a priority flow rate control valve.
The hydraulic pump is driven by an electric motor. The steering operation and cargo handling operation performed by the operator of the vehicle are respectively detected by sensors, and a controller performs chopper control of the electric motor based on the detection data by the sensors such that the discharge amount of the pressurized working oil by the hydraulic pump satisfies the working oil amount which is required by the power steering device and the cargo handling device.
The priority flow rate control valve comprises a valve spool which displaces in response to a differential pressure between a pressure in a pressure supply port of the priority flow rate control valve and a load signal pressure generated in the power steering device. The pressure in the load signal pressure port is led to the priority flow rate control valve via an orifice so as to act on an end surface of the valve spool. The power steering device is configured to raise the load signal pressure, when the working oil amount supplied thereto is in short supply with respect to an angular velocity of a steering wheel, so as to cause the valve spool to displace in a direction that increases the distribution ratio of the pressurized working oil to the power steering device.